Press

ABSTRACT

The present invention relates to a press which comprises a pressure vessel having an internal closure. The internal closure comprises a cover, a number of elements for transmitting forces in pressurised operation between the cover and the inner wall of the pressure vessel. Each element has a first contact surface adapted to fit a contact surface of the cover and a second contact surface adapted to fit a contact surface of the inner wall of the pressure vessel. Said elements are movable away from said contact surface of the cover and said contact surface of the inner wall of the pressure vessel in the direction of the longitudinal centre axis of the pressure vessel. The invention also relates to a method for opening a pressure vessel.

This application is a Divisional Application of U.S. application Ser.No. 10/479,681, filed Dec. 3, 2003, which is the national phase under 35USC § 371 of PCT International Application No. PCT/SE02/01210 filed onJun. 20, 2002, which designated the United States of America, and whichclaims priority from Sweden Patent Application No. SE 0102191-4 filed onJun. 20, 2001, the entire contents of all of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a press, which comprises a pressurevessel having an internal closure, and a method for opening a pressurevessel which is included in a press.

BACKGROUND ART

Many industrial manufacturing processes use presses, such ashigh-pressure presses. A common type of press, e.g. for machiningaluminium pieces, comprises a pressure vessel in which the actualpressing operation takes place and, which is provided with some type ofclosure, such as a cover. Traditionally, the cover has been screwed tothe wall of the pressure vessel by means of a threaded connection. Aftereach pressing operation when a processed material is to be removed fromthe press, the cover has to be unscrewed, which is a time-consumingprocedure.

U.S. Pat. No. 4,565,297 discloses an alternative embodiment of theclosure between cover and pressure vessel, several support segmentsbeing arranged between the cover and the pressure vessel. The sealingforce which originates from the cover is transmitted via these segmentsto the pressure vessel. In particular, the force transmission takesplace via parallel, specially designed contact surfaces. Thedisadvantage of the shown construction is that the segments are exposedto great strain at the risk of pressure concentrations arising incertain portions, which can lead to the segments cracking and needing tobe replaced earlier than desirable.

Another disadvantage is that any transverse forces acting on thesegments can make the segments slide upwards to the axis of the pressurevessel and, therefore, it has been necessary to arrange special lockingelements which with their vertical contact surfaces against the segmentsand the cover, respectively, prevent such a motion. In addition, theremoval of the cover with the purpose of reaching the inside of thepressure vessel seems to be a time-consuming procedure.

U.S. Pat. No. 2,821,325 discloses yet another variant of a closure forpressure vessels. Several segments having rounded contact surfaces arearranged between the cover and the pressure vessel. However, theconstruction is such that it is difficult to remove the cover. Anactuating lever is used to tilt the segments to a desired positionbefore the cover can be removed. Also this known technique thus involvesa time-consuming procedure.

SUMMARY OF THE INVENTION

In object of the present invention is to provide a press which allowssimple handling and which reduces the above-mentioned disadvantages.

Another object of the invention is to provide a method that allows thepressure vessel to be easily opened after a pressing operation has beencarried out.

These and other objects which will be evident from the followingdescription are achieved by means of a press and a method, which havethe features that are stated in the appended claims.

According to one aspect of the invention, a press is provided whichcomprises a pressure vessel having an internal closure. The internalclosure comprises a cover and a number of elements for transmittingforces in pressurised operation between the cover and the inner wall ofthe pressure vessel. Each force-transmitting element has a first contactsurface adapted to fit a contact surface of the cover and a secondcontact surface adapted to fit a contact surface of the inner wall ofthe pressure vessel. According to the invention, the pressure vessel isarranged in such a manner that the cover is allowed to assume twodifferent positions in the axial direction of the pressure vessel,namely a first position when the pressure vessel is pressurised and whensaid elements transmit forces from the cover to the inner wall of thepressure vessel, and a second position when the pressure vessel isessentially unpressurised and each element is movable away from saidcontact surface of the cover and said contact surface of the inner wallof the pressure vessel in the direction of the longitudinal centre axisof the pressure vessel.

Consequently, the invention is based on the insight that contactsurfaces of covers and pressure vessels do not need to be used as asupport for the elements in connection with the actual opening of thepressure vessel, and that the cover can be made movable in order tofacilitate a displacement of the elements from these contact surfaces.This allows a simple opening procedure since the cover is dimensioned sothat the elements can quickly be arranged in such a manner that theyhave no contact with said contact surfaces of pressure vessels andcovers.

It should also be understood that, according to at least one embodimentof the invention, said displacement of the elements can comprise thepartial steps of first separating said elements and said contact surfaceof the cover from one another and, subsequently, separating saidelements and said contact surface of the inner wall of the pressurevessel from one another.

Even if it is possible within the scope of the present invention to useboth straight contact surfaces and other shapes of the contact surfacesof said force-transmitting elements, cover and inner wall of thepressure vessel, it may be advantageous to have rounded contactsurfaces. By using contact surfaces of said elements which are curved ina longitudinal plane of section which is axial to the pressure vessel,relative motions can be permitted between cover and vessel wall withoutany risk of detrimental pressure concentrations on said elements. Insuch designs, said contact surfaces are suitably curved or rounded in alongitudinal plane of section which is axial to the pressure vessel sothat forces which are transmitted between the cover and the inner wallof the vessel provide an essentially uniformly distributed contactpressure between the cover and said force-transmitting element on theone hand, and said force-transmitting element and the inner wall of thevessel, on the other. In the rest of the description, the stress will beput on such curved contact surfaces. As stated above, it should beunderstood that the invention also can be used for other forms ofcontact surfaces.

In a press according to the invention, the pressure in the pressurevessel during a pressing operation is typically 50-2000 bar. During sucha pressing operation, the cover tends to bend axially upwards/outwardsand the wall of the pressure vessel tends to bend radially outwards. Thecurved contact surfaces take these deformations in the cover and thevessel wall into consideration, so that a moderate and uniformlydistributed contact pressure is obtained. When the cover and the vesselwall are deformed due to the internal overpressure, dimensionaladaptation takes place by a “rocking sliding motion” in the curvedcontact surfaces. Due to the curved contact surfaces, a large advantageis obtained in that the deformations of the vessel wall and the cover donot cause as large concentrations in the contact pressure as would havebeen caused by straight contact surfaces.

As mentioned above, each force-transmitting element has a first contactsurface that fits a contact surface of the cover and a second contactsurface that fits a contact surface of the inner wall of the vessel.Said first contact surface has thus suitably an essentially circular-arccross-section with a radius that essentially corresponds to the radiusof a circular-arc cross-section of the contact surface of the cover.Said second contact surface and the contact surface of the vessel alsohave the same agreement between the radii of the respective essentiallycircular-arc cross-sections.

Consequently, the curvature of the contact surfaces is suitably based oncalculations of the deformation of the cover and the vessel wall, therespective curvatures being made so as to obtain the maximum evencontact pressure between the force-transmitting elements and the coverand the vessel wall, respectively. In spite of the changes in anglesthat arise between the cover and the vessel wall, the even contactpressure is to be maintained.

The advantageous shape can be made either convex or concave. It is thuspossible to form said force-transmitting elements so that said first andsecond contact surfaces bend outwards to the cover and the wall of thepressure vessel, respectively. Alternatively, the high-pressure presscan be adapted for elements having inwardly curved contact surfaces. Yetanother alternative is to let one of said first and second contactsurfaces bend inwards and the other contact surface bend outwards.

The force-transmitting elements together form an annular configurationin the circumferential direction of the pressure vessel. Eachforce-transmitting element thus suitably constitutes a toroidal part.When opening the cover, said elements are removed by moving themradially towards the centre axis of the pressure vessel and are thusremoved from the contact surfaces of the cover and the pressure vesselwall, respectively, which will be described below in more detail. Thismeans that in the annular configuration which said force-transmittingelements form, there should be sufficient space between two adjacentelements in order to move these radially inwards to the centre axissince the circumference of the annular configuration decreases nearerthe centre axis. The number of force-transmitting elements is preferablyat least three, for instance at least four, in particular six. However,as an alternative force-transmitting elements can be used, which areonly two in number. In this case, the force-transmitting elements arebendable.

In this application text, the centre axis is defined as the straightcentre axis which runs in the altitude of a cylinder. Theforce-transmitting elements are essentially adapted to transmit axialforces.

According to the invention, the press is designed so that the cover ismovable between a first and a second position. For a vertically arrangedpressure vessel, the cover, either a bottom cover or a top cover, isvertically adjustable. This adjustability facilitates the removal andthe mounting of said elements. In the press according to U.S. Pat. No.4,565,297, there is no such mechanism since the plane contact surfacesallow the segments to be moved in a direction obliquely upwards to thecentre axis of the pressure vessel without vertically adjusting thecover. However, it is necessary that special locking elements bearranged between the segments and the cover in order to prevent thesegments from undesirably sliding towards the centre axis when they areexposed to transverse forces. It should also be noted that if a pressurevessel in a press according to the invention is arranged horizontally,i.e. the centre axis extends horizontally, said first and secondposition of the cover would be separated in the horizontal direction.

In the press according to the present invention, the rounded shape ofthe contact surfaces has such an inherent property that the elements toa certain extent are prevented from being undesirably radially movedtowards the centre axis, in contrast to prior-art smooth, plane contactsurfaces. Thus, it is not necessary to use an extra locking element forthe invention. As will be evident from the following, a filling elementbetween the force-transmitting elements and the cover, however, presentsan advantageous embodiment of the invention.

Although it is not necessary to use any supplementary locking element,it may be desirable to ensure that undesired motion of said elements inthe direction of the centre axis caused by transverse forces essentiallydoes not occur, i.e. it is not desirable to allow each element with itscentre of mass to be moved in an uncontrolled manner towards the centreaxis. However, it is desirable to allow the sliding motion of theforce-transmitting elements rocking round the centre of mass so thatthey reach the correct position before a pressing operation. Thus, theclosure can be such that a side of each force-transmitting elementfacing the centre axis is in contact with a portion of the cover, thecover per se blocking lateral motion of the elements.

When a pressing operation is completed, the finished material is to beremoved from the pressure vessel, which means that the cover first is tobe removed. To allow removal of the cover, the force-transmittingelements are first removed. As mentioned above, these are preferablyprevented from moving laterally by a portion of the cover. The solutionis first to lower the cover enough so that there is no obstacle tolateral movement of said force-transmitting elements. Like in atranslational motion, the force-transmitting elements are then drawntowards the centre axis of the pressure vessel, for example, by means ofactuators, such as hydraulic pistons, motor-driven ball bearing screws,pneumatic or mechanical actuators, after which the cover, and preferablythe force-transmitting elements arranged thereon, are lifted away fromthe pressure vessel so that the inside of the pressure vessel becomesaccessible. The force-transmitting elements are thus removed from thatcontact surface of the cover which is used during the actual pressingoperation to a position above said contact surface.

As mentioned above, the first contact surface of said elements is thusduring a pressing operation adapted to abut against said contact surfaceof the cover, which is a first contact surface of the cover. Accordingto at least one embodiment of the invention, the cover also comprises asecond contact surface against which the first contact surface of saidelements is adapted to abut after a pressing operation when lifting thecover, or before a pressing operation when lowering the cover.

The method described above applies to a top cover. As regards a bottomcover, the removal is carried out vertically inversely, i.e. first thecover is elevated, said elements are moved inwards to the centre, andthe cover is then removed by being lowered.

Alternatively, a filling element can be used, which is arranged betweena side of each force-transmitting element facing the centre axis of thepressure vessel and the cover. This filling element which contributes toretaining said force-transmitting elements and preventing radialdisplacement, suitably comprises one single annular piece. The fillingelement is thus a supplementary protection. However, theforce-transmitting elements will essentially rock unlike segments havingstraight contact surfaces which tend to slide out of position withoutany supplementary locking. Even though the filling element is notnecessary, it exhibits an important advantage in this context. Accordingto the preceding alternative without a filling element, it is necessaryto lower the cover enough to allow the force-transmitting elements to bepulled radially inwards to the centre axis away from the contact surfaceof the cover. If the portion of the cover that constitutes this blockingfunction is just as high as each force-transmitting element, this meansthat the cover should be lowered a distance corresponding to thisheight, which typically can be 100-200 mm. The use of filling elementscertainly involves that they have to be lifted to make it possible toremove the force-transmitting elements but, on the other hand, it is notnecessary to lower the cover more than a few millimetres, typically lessthan 20 mm. The distance also depends on how much the contact surfacesare curved.

A top cover is elevated and lowered preferably automatically between theupper position, in which the cover is located in the pressurised stateof the press, and the lower position, in which the cover is located whenthe press is not pressurised. In an unpressurised state, the cover isthus located in the lower position, each force-transmitting element withits first contact surface abutting against the contact surface of thecover. However, there will be a gap between the second contact surfaceof each force-transmitting element and the contact surface of the innerwall of the pressure vessel. When pressurizing the pressure vessel, theoverpressure generated therein will affect the cover so that it movesupwards, the second contact surface of each force-transmitting elementbeing brought in contact with the inner wall of the pressure vessel. Ina corresponding way, the contact will cease when the pressure after thepressing operation is relieved and the cover is lowered again. Eventhough this described motion of the cover to a large extent isautomatic, for example, hydraulic pistons can also be used for thispurpose in order to obtain extra safety. These hydraulic pistons arepreferably also used for removing the cover from the press so that thecontents of the pressure vessel become accessible.

Alternatively, said gap can instead be formed between the cover and theforce-transmitting elements, for example, by hydraulic pistons retainingthe force-transmitting elements in contact with the contact surface ofthe vessel wall, while the cover is lowered after the pressing operationand is lifted (mechanically or by means of the internal pressure) beforea new pressing operation. With the aid of retaining means, such ashydraulic, pneumatic, mechanical or electrical means, said elements canthus be adapted to be retained in essentially the same position whilethe cover is lowered from the upper position to the lower position inorder to cause said elements to move away from the contact surface ofthe cover. The displacement of the cover must be considered to beequivalent to displacement of the elements themselves since the mutualrelation is the same in both cases, i.e. the first contact surface ofthe elements and the contact surface of the cover are removed from oneanother.

According to at least one embodiment of the invention, the removal ofthe contact surfaces of the force-transmitting elements from the contactsurface of the cover and the contact surface of the inner wall of thepressure vessel can thus be carried out in two separate steps. In afirst stage, the elements are thus removed from the contact surface ofthe cover by this being lowered, i.e. moved from its first position toits second position, and in a subsequent second stage the elements areremoved from the contact surface of the inner wall of the pressurevessel by each element in its totality being made to move towards thecentre axis of the pressure vessel.

The force-transmitting elements having the curved contact surfacesaccording to the invention are preferably manufactured by turning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a high-pressure press according to thepresent invention.

FIG. 2 is a schematic part-sectional view of a pressure vessel with aninternal closure, which is comprised in a press according to anembodiment of the present invention.

FIG. 3 schematically shows the pressure vessel in FIG. 2 when it isarranged to be opened.

FIG. 4 is a schematic part-sectional view of a pressure vessel with aninternal closure, which is comprised in a press according to anotherembodiment of the present invention.

FIG. 5 schematically shows the pressure vessel in FIG. 4 in anunpressurised state.

FIG. 6 is a schematic part-sectional view of a pressure vessel with aninternal closure, which is comprised in a press according to yet anotherembodiment of the present invention.

FIG. 7 schematically shows the annular configuration that is formed bythe force-transmitting elements comprised in the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a high-pressure press 10 according tothe present invention. The high-pressure press 10 comprises a circularcylindrical pressure vessel 12 which is lowered into a cavity. The lowerend of the pressure vessel 12 is located on a support 14 at the bottomof the cavity. An upper portion of the pressure vessel extends above thefloor or ground level 16. A support arrangement 18 for a hydraulicdevice is attached to the floor. The hydraulic device comprises ahydraulic unit 20 which controls the vertical motion of four hydraulicpistons 22 for lifting and lowering a cover which closes the pressurevessel. The hydraulic device also comprises hydraulic pistons (notshown) for displacing force-transmitting elements, which will bedescribed in the following. Furthermore, a hydraulic piston 23 isillustrated, the function of which, among other things, is to remove afilling element, which is illustrated in connection with the embodimentshown in FIGS. 4 and 5.

FIG. 2 schematically shows a longitudinal part-sectional view of apressure vessel 30 having an internal closure, the pressure vessel beingcomprised in a press according to an embodiment of the presentinvention. The upper portion 32 of the pressure vessel 30 has anenlarged radius. The pressure vessel comprises a wall 33, the inside 34(also named inner wall) of which in this enlarged portion 32 is cut outso as to form a recess 36. The inner wall 34 is along the recess 36essentially parallel to the outside of the pressure vessel 30 with theexception of the upper portion of the recess. In the upper portion ofthe recess 36, a contact surface 38 is formed, which is curved in theplane shown in the partial cross-sectional view. Since the pressurevessel 30 is cylindrical, the wall 33 of the pressure vessel 30 iscurved round its longitudinal centre axis, i.e. in a transverse plane ofsection through the pressure vessel 30. This also applies to saidcontact surface 38 which is thus curved in two planes.

A solid cover 40 having a flat bottom surface is arranged in thepressure vessel 30 and is provided with a seal (not shown) that issuitable for this purpose. Similarly to the inner wall 34 of thepressure vessel 30, the cover 40 has a contact surface 42 which iscurved in the longitudinal plane of section shown through the pressurevessel 30. A force-transmitting element 44 is arranged between the innerwall 34 of the pressure vessel 30 and the cover 40. Theforce-transmitting element 44 has a first lower contact surface 46 and asecond upper contact surface 48 which are curved in the shown plane. Thelower contact surface 46 is fitted into the contact surface 42 of thecover 40 and the upper contact surface 48 is fitted into the contactsurface 38 of the inner wall 34. For optimal fitting, the contactsurfaces 38, 48 and 42, 46, respectively, have essentially the sameradii of curvature in the shown plane. In this Figure, the radii ofcurvature of the first contact surface and the second contact surface ofthe force-transmitting element 44 are also essentially of the same size,i.e. 100 mm. Based on calculation of the deformation of the cover 40 andthe vessel wall 33, the contact surfaces 38, 42, 46, 48 are formed so asto obtain the maximum even contact pressure. Thus, the size (alsorelative proportions) of the radii can vary depending on press andapplication.

The force-transmitting element 44 is with its essentially verticallateral surfaces 50, 52 in contact with essentially vertical surfaces54, 56 of the cover 40 and the inner wall 34 of the pressure vessel 30,respectively. The vertical surface 54 of the cover 40 prevents theforce-transmitting element 44 from sliding out of position. The pressurevessel 30 shown in FIG. 2 is pressurised, for example, to 1000 bar,which means that the internal overpressure presses the cover 40 axiallyupwards, which, in its turn, transmits the axial forces via theforce-transmitting element 44 to the pressure vessel wall 33. Due to thecurvature of the contact surfaces 38, 42, 46, 48 according to theinvention, a uniformly distributed contact pressure is provided.

In addition, the cover 40 has in an upper portion a further contactsurface 58 and the vessel wall 33 has a shoulder 60 protruding towardsthe centre. The functions of these parts 58 and 60 will be described inconnection with FIG. 3.

FIG. 3 schematically shows the pressure vessel in FIG. 2 when preparedto be opened, the same reference numerals being used for equivalentparts in the Figures. After a completed pressing operation, the cover 40is lowered in the pressure vessel 30 a distance corresponding to theheight of the force-transmitting elements 44, while these are retainedin the vertical position by means of suitable equipment such ashydraulic pistons (not shown), the first contact surface 46 of theforce-transmitting elements thus being removed from the contact surface42 of the cover by lowering the cover. The circumferential shoulder 60which protrudes from the vessel wall 33 functions as a support for thecover 40 after this has been lowered. Subsequently, theforce-transmitting elements 44 can be removed by hydraulic pistons (notshown) from the wall 33 of the pressure vessel 30 radially inwards tothe centre axis of the pressure vessel 30. Consequently, the lowercontact surface 46 of the force-transmitting element 44 will restagainst that contact surface 58 of the cover 40 which is formed in theupper portion of the cover 40, as shown in FIG. 3 (dashed linesillustrate the position of the force-transmitting element before thedisplacement). Then the cover 40, with force-transmitting elements 44resting thereon, is lifted out of the pressure vessel 30 by means ofhydraulic pistons (not shown), after which the cover 40 is suitablyremoved sideways from the opening of the pressure vessel 30. Thefinished material can now be removed and new material be supplied to thepressure vessel 30. The opposite procedure follows, in which the cover40 with force-transmitting elements 44 arranged thereon is lowered intothe pressure vessel 30; the elements 44 are moved towards the vesselwall 33, the vessel 30 is pressurised and the cover 40 is lifted towardsthe elements 44. The elements 44 will slide into the correct angle dueto the curvature of the contact surfaces 38, 42, 46, 48 according to theinvention.

FIG. 4 schematically shows a part-sectional view of a pressure vessel 70with an internal closure, which is comprised in a press according toanother embodiment of the present invention. The Figure shows both theupper portion 72 and the lower portion 74 of the pressure vessel;however, the middle portion is removed for reasons of clarity. In thepressure vessel 70, an upper cover 76 and a lower cover 78 are thusarranged, between which a space is pressurised for machining a material.The upper cover 76 exhibits, like the cover in FIG. 2, a contact surface80 which is curved in a longitudinal plane of section which is axial tothe pressure vessel 70, against which contact surface abuts the lowercontact surface 84 of a force-transmitting element 82. As in FIG. 2, theupper contact surface 86 of the force-transmitting element 82 is infitted contact with a contact surface 88 of the inner wall 90 of thepressure vessel 70. The wall 92 of the pressure vessel 70 comprises acircular shoulder 94 that limits the downward motion of the upper cover76 in the pressure vessel 70.

At least to a certain degree, the curved contact surfaces 80, 84, 86, 88prevent the force-transmitting element 82 from moving radially towardsthe centre axis of the pressure vessel 70. Moreover, as a supplementaryprotective measure, a filling element 96 is positioned between theinside of the force-transmitting elements 82 and the upper cover 76,which filling element 96 has essentially the same height as theforce-transmitting element 82. A hydraulic piston 98, which extendsthrough the upper cover 76 and the filling element 96, is attached tothe side of the force-transmitting element 82 facing the centre axis.The inclination of the hydraulic piston 98 shows that theforce-transmitting element 82 is movable in a diagonal directionupwards/inwards. The filling element 96 is formed as a continuous ringround the upper cover 76. The filling element 96 is provided with slotsso that it can be slipped onto the hydraulic pistons 98 which areattached to the force-transmitting elements 82. FIG. 4 thus shows across-section through, among other things, such a slot. As is evidentfrom the Figure, a duct 100, through which runs the hydraulic piston 98,is formed in the upper cover 76. The inner diameter or width of the duct100 is larger than the outer diameter or width of the hydraulic piston98 in order to allow displacement of the upper cover 76 in the verticaldirection.

Inside the pressure vessel 70, a furnace (not shown) is adapted to heatthe material to be machined. Under the upper cover 76, a cooler plate102, which is protective against the temperature rise, is arranged withducts for cooling water. A rubber seal 104 is arranged round the coolerplate 102 and seals against both the inner wall 90 of the pressurevessel 70 and the cover 76. Furthermore, the rubber seal 104 abutsagainst a metal ring 106 having a triangular cross-section, which metalring 106 prevents the rubber seal 104 from extruding between the cover76 and the inner wall 90 of the pressure vessel 70. Yet another seal 108is arranged below the rubber seal 104. This further seal 108 protectsthe rubber seal 104 against harmful ascending gases and also serves tohold the rubber seal 104.

A corresponding construction with a cooler plate 102 and seals 104, 106,108 is also found in the lower portion 74 of the pressure vessel 70, asshown in FIG. 4. In the lower portion 74 of the pressure vessel 70,there is also a force-transmitting element 110 between the lower cover78 and the inner wall of the pressure vessel. The distribution ofcontact pressure thus corresponds to that described above. If desirable,the stiffness of the force-transmitting element 110 can be reduced byforming slots therein.

Whereas FIG. 4 illustrates a typically pressurised state of the pressurevessel, FIG. 5 schematically shows the upper portion 72 of the pressurevessel 70 in FIG. 4 in an unpressurised state, the same referencenumerals being used for equivalent parts. The hydraulic piston 98retains the force-transmitting element 82 against the inner wall 90 ofthe pressure vessel 70, while the cover 76 is lowered after a completedpressing operation. The cover 76 is lowered only a few millimetres untilit meets the shoulder 94 of the wall 92 of the pressure vessel 70. Thus,a gap is formed between the lower curved contact surface 84 of theforce-transmitting element 82 and the contact surface 80 of the cover76. The duct 100 through the cover 76, in which the hydraulic piston 98runs is sufficiently broad for the hydraulic piston 98 to maintain itsinclination also when the cover 76 is lowered. Due to the use of thefilling element 96 (instead of a broader upper portion of the cover asin FIG. 2), it is not necessary to lower the cover 76 a distancecorresponding to the height of the force-transmitting element 82. Thefilling element 96 is lifted straight upwards, preferably by means ofhydraulic pistons (not shown) in such a manner that theforce-transmitting element 82 can be freely pulled out diagonally in thelongitudinal direction of the shown hydraulic piston 98, after which thecover 76 and the force-transmitting element 82 can be lifted up so thatthe inside of the pressure vessel 70 becomes accessible.

FIG. 6 schematically shows a part-sectional view of a pressure vessel120 which has an internal closure and is comprised in a press accordingto yet another embodiment of the present invention. The pressure vessel120 shown in FIG. 6 largely corresponds to the pressure vessel shown inFIG. 5. However, there is a difference. The lower contact surface 124 ofthe force-transmitting element 122 and the corresponding contact surface126 of the cover 128 are curved in the opposite direction. This meansthat in the press in FIG. 6 these surfaces are concave seen from thecentre axis of the pressure vessel, whereas in the press in FIG. 5 thesurfaces are convex seen from the centre axis of the pressure vessel.

FIG. 7 schematically shows the annular configuration 140 which is formedby the force-transmitting elements included in the invention. Thus, sixseparate force-transmitting elements 142 are shown, each having theshape of a circular arc. The position of the elements 142 when thepressure vessel is pressurised is shown with unbroken lines, while theposition of the elements 142 when the cover is ready to be lifted up isshown with dashed lines. As is evident from the Figure, the elements 142are moved radially inwards after a completed pressing operation so thatthe cover can be removed and the machined material taken out of thepressure vessel.

Although some embodiments have been described above, the invention isnot limited thereto. It should thus be understood that manymodifications and variations can be provided without deviating from thescope of the present invention which is defined in the appended claims.

1. A method for opening a cylindrical pressure vessel having an internal closure which includes a cover and a number of force-transmitting elements adapted to abut against a contact surface of the cover and a contact surface of an inner wall of the pressure vessel, which method comprises: relieving pressure from the pressure vessel; releasing said force-transmitting elements by moving the cover in a longitudinal direction of the pressure vessel, from a first position to a second position; translating said force-transmitting elements away from said contact surface of the cover and said contact surface of the inner wall of the pressure vessel inwards toward a longitudinal center axis of the pressure vessel; and removing the cover and said force-transmitting elements.
 2. The method as claimed in claim 1 wherein said step of moving the cover from a first position to a second position comprises lowering the cover from an upper position to a lower position, and the step of removing the cover comprises lifting it away from the pressure vessel.
 3. The method as claimed in claim 2 wherein the step of moving said force-transmitting elements comprises retaining said force-transmitting elements in substantially a same position, while lowering the cover from the upper position to the lower position.
 4. The method as claimed in claim 3 wherein the step of moving said force-transmitting elements comprises first separating said force-transmitting elements and said contact surface of the cover from one another and, subsequently, separating said force-transmitting elements and said contact surface of the inner wall of the pressure vessel from one another.
 5. The method as claimed in claim 2 wherein the step of moving said force-transmitting elements comprises placing the force-transmitting elements on another contact surface of the cover, and the step of lifting the cover comprises lifting the cover with the force-transmitting elements positioned thereon.
 6. The method as claimed in claim 1 wherein the step of moving said force-transmitting elements is preceded by the step of removing one or more filling elements from between a side of each force-transmitting element and the cover.
 7. The method as claimed in claim 1 wherein moving the cover step is performed automatically without any external action when pressure is relieved from the pressure vessel.
 8. The method as claimed in claim 1 wherein the step of releasing said force-transmitting elements comprises releasing said force-transmitting elements from a form-fit state.
 9. A method, comprising: translating a force-transmitting element of a closure of a pressure vessel from a lock position to a release position; moving the closure from a first position to a second position within the pressure vessel, thereby locking the force-transmitting element in the lock position; pressurizing the pressure vessel; and transmitting pressurizing forces from a contact surface of the closure to a contact surface of a wall of the pressure vessel via the force-transmitting element.
 10. The method of claim 9, further comprising: placing a product to be subjected to pressure into the pressure vessel; moving the closure into the opening of the pressure vessel; releasing the pressure from the pressure vessel; moving the closure from the second position to the first position; translating the force-transmitting element from the lock position to the release position; removing the closure from the pressure vessel; and removing the product from the pressure vessel. 